1. Field of the Invention
The present invention relates to print media edge detection, and more particularly, to a print media edge detection method and apparatus capable of performing marginless edge printing by improving edge detection ability.
2. Description of the Related Art
When marginless printing on a top, bottom, right, or left edge position of a print medium is performed in a hard copy apparatus, edge printing may not be performed on an exact position due to failure of an exact edge position detection. As an example, when printing on the bottom edge position is performed, a jump effect may occur, by which a sheet of print media transported into a printing zone by feeding rollers is transported farther than a print media set distance due to a print media escape speed when the sheet of print media is freed from the feeding rollers. The jump effect occurs since the sheet of the print media out from the feeding rollers cannot be strongly held only with discharging rollers. As such, printing quality may be deteriorated due to the occurrence of a feeding error caused by the jump effect.
To resolve this problem, conventional print media edge detection methods are disclosed in U.S. Pat. Nos. 6,352,332 and 6,079,892.
FIGS. 1 and 2 are graphs to explain a print media edge detection method disclosed in U.S. Pat. No. 6,352,332.
With reference to FIG. 1, measured reflectance data 301 according to a position is obtained by scanning a front surface of a sheet of print media using an optical sensor to detect an edge position of the sheet of print media. With reference to the data 301, the reflectance is about 3,300 A/D counts on most of the sheet of print media, gradually decreases near from the edge position of the sheet of print media, dramatically decreases outside of the edge position of the sheet of print media, and is about 490 A/D counts on a pivot. A shape curve 302 in accordance with Equation 1 is formed by calculating a high average reflectance and a low average reflectance from a plurality of sample data and considering a field of view of the optical sensor.slope=(high average reflectance−low average reflectance).div.field of view.  Equation 1
If the shape curve 302 is moved in an arrow mark direction with a distance corresponding to a predetermined error value to find out a real edge position using a reference edge position, a graph 300′ with a moved shape curve 302′ can be obtained as shown in FIG. 2. With reference to FIG. 2, in the conventional method, a position corresponding to an edge 303 when the reflectance suddenly decreases, that is, 250 (* 1/600 inch) is set as the edge position.
However, in the print media edge detection method disclosed in U.S. Pat. No. 6,352,332, when the shape curve 302′ is formed, a slope start position is not accurate, and a position variation range of the edge 303 can be wide.
FIG. 3 is a graph to explain a print media edge detection method disclosed in U.S. Pat. No. 6,079,892. With reference to FIG. 3, a detection voltage is obtained according to the amount of feeding print media. A standard voltage Vsa of a print medium A is obtained by multiplying a predetermined constant number C by a voltage difference between a maximum reflectance Vm1 of the print medium A and a voltage Vp detected on a platen, and another standard voltage Vsb of a print medium B is obtained by multiplying the predetermined constant number C by a voltage difference between a maximum reflectance Vm2 of the print medium B and the voltage Vp. Here, the constant number C is a value in proportion to the amount of light reflected from the print medium. When the print medium is not fed, C=0, and when all the light beam irradiated from a sensor is reflected since the print medium is perfectly fed, C=1. The C value is set to an appropriate value between 0 and 1, i.e., for example, 0.3.
In the print media edge detection method disclosed in U.S. Pat. No. 6,079,892, when margin printing on the print medium is performed, a real time voltage value can be obtained from the amount of reflected light by irradiating the light beam on the print media edge position using an optical sensor, and if a voltage value approaching the standard voltage Vsa or Vsb is obtained, feeding of the print medium is stopped, and printing is performed.
However, in the print media edge detection method disclosed in U.S. Pat. No. 6,079,892, since the C value is represented only with a value related to the reflectance, exact data about the C value is not given, and a variation range of the standard voltage Vsa or Vsb is wide, stability is low.